Visual Glossary

Flash flood

Flash floods are brief, but torrential floods. They usually result from exceptionally heavy rainfall falling in areas with steep slopes over a short interval of time. The excess water overflows stream banks carrying a huge load of muddy debris. The force of the fast-moving bouldery slurry may cause severe damage where flood waters meet man-made structures.

A road sign warning of the danger of flash floods lies by the roadside along with boulders left behind after the floods of July 14, 1999 in Death Valley National Park. Photo by Gerry Wolfe, NPS.